Successive approximation analog-to-digital converters (ADCs) convert a sampled level of a continuous or analog waveform into a digital representation through what is essentially a search of possible quantization levels, in order to converge on a digital value corresponding to conversion of the sampled level of the waveform. Successive approximation ADCs often employ switches to share charge between and among capacitors. ADCs are used in many circuits and systems, including, for example, sigma-delta modulators, which are typically present in wireless access terminals of cellular networks.
Progressively higher levels of system integration are desired in many electronic systems, including wireless access terminals, because integration offers lower production costs, allows more functions to be packed into smaller footprints and volumes, and improves performance as a result of increased speed and reduction in power consumption. Complimentary Metal-Oxide Semiconductor (CMOS) technology is currently widely used in making electronic devices. The need for high levels of integration is driving CMOS technology deeper into nanometer scale of fabrication. At this time, CMOS devices may be fabricated using 65 nm and even smaller feature-size devices. The scale of CMOS devices is likely to continue to decrease in the future. Unfortunately, good CMOS switches are not always readily available in deep submicron low-voltage fabrication processes.
Therefore, there is a need in the art to reduce the number of circuit-level CMOS switches in circuit designs, possibly replacing the circuit-level switches with inverters and logic gates. There is also a need in the art for increased operational speed of comparators, including comparators used in ADCs. There is a further need in the art for electronic devices, including wireless access terminals, employing the ADCs with reduced numbers of CMOS switches, and employing fast comparators.